Notice keyint=250 when it should be keyint=25. This means I can't force a keyframe every second. Playing back the video, I can only seek every 3 seconds, not every second.

Workaround: In the libx264 project under common/common.c, change "param->i_keyint_max" from 250 to 25, recompile libx264 and re-run the encoder. The result is there's a keyframe every second as expected and now I can seek to any position in the video.